The default algorithm to use for hashing if no algorithm is provided.
This may change in newer PHP releases when newer, stronger hashing
algorithms are supported.

It is worth noting that over time this constant can (and likely will)
change. Therefore you should be aware that the length of the resulting
hash can change. Therefore, if you use PASSWORD_DEFAULT
you should store the resulting hash in a way that can store more than 60
characters (255 is the recomended width).